1. Field of the Invention
The present invention relates generally to traveling grate machines for thermally treating particulate materials, such as, for example, iron ore or zinc ore pellets. More particularly, the present invention relates to apparatus and methods for removing and replacing selected pallet cars in a traveling grate machine xe2x80x9con-the-flyxe2x80x9d, that is, while the traveling grate machine is in operation.
2. Background of the Related Art
Traveling grate machines of the type shown in FIGS. 1-4, generally designated 2, have a plurality of pallet cars 4 which receive a burden 5, for example. iron ore from a feed means 9. The pallet cars travel on a horizontally extending, top strand 6 through an updraft drying zone 12, a downdraft preheating/drying zone 13 and, thence, to a high temperature firing zone 14 to thermally condition the particulate iron ore pellets in a desired manner. A first cooling zone 15 and a second cooling zone 16 in an updraft manner complete the thermal treatment of the particulate matter carried by the pallet cars 4. At the end of the upper strand 6, at the idler sprocket end 11, the heat-treated burden is dumped by gravity from the pallet cars which then travel in an upside-down, empty condition along a horizontally extending bottom strand 8 to return to the drive sprocket 10 end of the traveling grate machine 2. Due to the severe environment of the traveling grate machine, routine maintenance is required on the pallet cars 4. Currently, this maintenance is accomplished by first stopping the machine and removing and replacing the pallet car or cars needing maintenance. It is undesirable to stop the traveling grate machine for such maintenance requirements for several reasons. Stopping the machine modifies the thermal process causing degradation of the product quality. Because the process involves very high temperatures, pallet car components in a pallet change condition are subject to higher temperatures for a prolonged time period, for example, in the preheat and firing zones of the traveling grate machine, which results in a lower pallet car life. Finally, there is a loss of production output when the traveling grate machine is stopped for the purpose of pallet car changeover or replacement.
The present invention eliminates these problems enumerated above by providing an apparatus and method whereby pallet cars are changed on-the-fly, that is, without stopping the machine. Hence, the present invention provides for uniform quality of the thermally treated ore while increasing productivity of the machine and eliminating the problem of overheating of pallet cars heretofore required in prior art pallet changeover methods.
Briefly stated, the present invention is directed to an apparatus and method for changing pallet cars on-the-fly in a traveling grate machine. The pallet cars are of the type having supporting wheels thereon for travel on the traveling grate machine which includes spaced-apart outer and inner guide rails located at each side of the machine for guiding the wheels of the pallet cars along a top strand and, thence, to a bottom or return strand, and along intermediate curved end portions joining the top and bottom strands. Further, the traveling grate machine is of the type which includes drive sprocket means positioned at one of said intermediate curved end portions for engaging and driving rollers, adjacent to the wheels, carried by the pallet cars for causing movement of the pallet cars along the top and bottom strands of the machine.
The apparatus for changing the pallet cars comprises first hinged sections of outer guide rails located at the drive sprocket means adjacent to the bottom strand. A means for pivotally moving the first hinged sections of outer guide rails from a locked position to an open position is provided whereby in an open position a selected first pallet car may be removed from the drive sprocket means and inner guide rails. Also provided are laterally spaced-apart second hinged sections of outer guide rails located at the drive sprocket means adjacent to the upper strand. Means for pivotally moving the second hinged sections of outer guide rails from a locked position to an open position is also provided, whereby in an open position a replacement pallet car may be inserted on the sprocket means and against the inner guide rails in a position previously occupied by said selected first pallet while the sprocket means rotates. The apparatus further preferably includes a movable shuttle car for receiving and supporting the selected first pallet car from the first hinged sections of outer guide rails and for transporting the pallet car so removed to a remote location for pickup by a crane. Also provided is a pallet car insertion means comprising a structural frame pivotally mounted to a separate structure located adjacent to the drive sprocket means for supporting and lifting a replacement pallet car into a position whereby the replacement pallet car may be inserted on the drive sprocket means as the structural frame pivots to an uppermost position. The pallet car insertion means preferably includes means for electro-magnetically holding the replacement pallet car thereto as the structural frame pivots to an uppermost position.
The presently preferred method for changing pallet cars according to the present invention comprises the steps of: providing a first hinged section of outer guide rails located at the drive sprocket means adjacent to the bottom strand of the traveling grate machine; opening the first hinged section of guide rails; removing a first selected pallet car positioned at the first hinged section as the drive sprocket means rotates to provide an open space between a pair of adjacent pallet cars; closing said first hinged section of guide rails after said pallet car has been removed to permit an adjacent trailing car to ride therealong; providing a second hinged section of outer guide rails spaced from said first hinged section located at the drive sprocket means adjacent the upper strand of the machine; rotating the drive sprocket means to index the open space formerly occupied by the removed pallet car to a position adjacent said second hinged section of guide rails; opening the second hinged section; inserting a replacement pallet car into the space formerly occupied by the removed car; and closing the second hinged section of outer guide rails, whereby the pallet car replacement is accomplished without halting movement of the drive sprocket means.